Solder paste is printed on a printed circuit board that is mounted on an electronic device by a screen printer and the process of printing solder paste on a printed circuit board using a screen printer is as follows. A screen printer loads a printed circuit board on a table for fixing the printed circuit board and aligns a stencil on the printed circuit board with the apertures of the stencil on the pad of the printed circuit board. Thereafter, the screen printer prints the solder paste onto the printed circuit board by depositing the solder paste through the apertures of the stencil using a squeegee. The screen printer then separates the stencil and the printed circuit board from each other.
The shape of solder pastes printed on a printed circuit board may be inspected through SPI (Solder Paste Inspection). SPI is a technique that obtains a 2D or 3D image of the solder pastes printed on the printed circuit board through an optical technology and inspects the shape of solder pastes printed on the printed circuit board from the obtained image.